Many piping system applications in chemical and natural resource recovery industries involve the handling of corrosive, erosive, scaling or otherwise hard-to-handle fluids. One economic approach to handling these difficult fluids is to cover or line the interior of low cost, non-fluid-resistant pipe with a fluid-resistant liner. The pipe material, such as low carbon steel, provides low cost structural support for the costlier and/or structurally inadequate liner. Although some thin liners or coatings can be sprayed on, more severe applications (e.g., erosive slurries) or other factors may require thicker liners. One type of thicker, fluid resistant liners is composed of a low tensile strength or brittle material, such as cement.
These brittle lining materials must be able to structurally withstand the severe applications at the piping joints. The severe applications tend to chip, spall, crack, pit, and delaminate the lining at these critical points. These structural problems become especially troublesome at brittle liner edges in certain types of joints. For example, removable joints may need to be periodically opened for inspection, cleaning, or testing. Opening and resealing adds further structural demands on the brittle liner edges at these critical areas.
The primary objectives of a removable lined pipe joint are to: 1) allow assembly of lined pipe sections; 2) seal the assembled pipe sections; 3) prevent exposure of non-fluid-resistant piping material to a variety of harsh flowing materials; 4) structurally withstand a variety of operating environments; and 5) allow joint disassembly and reassembly. The lined pipe connector apparatus at these joints should also be rugged in construction, easy to maintain, safe, reliable, and low in cost.
Current lined pipe joints may perform some of these objectives well, but other objectives may be accomplished poorly or not at all. Connectors having engaged or sizably loaded liner seals satisfy these objectives for piping lined with metal or elastomeric materials, but are not practical for fragile or brittle liners. Engaged (e.g., threaded) loads and liner end surface preparations (e.g., machining to obtain a smooth sealing surface finish) can impose high stresses on the brittle liner edges, resulting in damage to the brittle liner and failure at the piping joint.
In addition to a piping seal (e.g., pipe threads), conventional brittle lined pipe connectors add a separate easily deformable (soft) material at the interfacing edges of the liner. The soft liner seal requires less load on the liner to prevent exposure of the non-resistant pipe at the joint to the harsh fluid. The added liner seal must also be a primary seal, since soft liner seal failure exposes the non-fluid-resistant pipe material to the harsh fluids, causing long term piping failure even if the piping seal is not leaking.
One type of liner edge seal places a putty-like (i.e., plastic flowing or semi-fluid) material at the liner edges. The putty-like material is generally initially unsupported. The edge seal material may harden, such as a cement slurry. However, the use of the putty-like material, especially a hardenable slurry, limits or precludes disassembly capability.
Using the putty-like seal may also require internal access after assembly. Access may be required for patching, removal of extruded putty-like material, or inspection. Although the plastically flowing material limits stress on a brittle liner (i.e., only a small liner seal load is needed to plastically flow the putty-like material), the unsupported putty may not reliably seal the liner edges or be able to withstand severe applications, such as handling an erosive fluid.
Another type of sealed edge liner joint uses a soft elastomeric material at the joint lining interface for the liner end seal. A groove or retaining surface may be added to the lining material to provide support for this type of deformable seal, in contrast to a putty-like material which would not be retained by a groove. In addition to anchoring the elastomeric material, the groove can provide space for seal distortion under load.
However, liner end sealing surfaces may be rough, shrink or otherwise be out of position to be sealed by the elastomeric element. The grooves and elastic deformation may also apply excessive seal loads to a brittle liner. A brittle liner may also require special sealing surface preparation to effect a seal within the tolerances and limited seal load capability of a fragile liner material.
Both of the conventional brittle liner edge seal methods require an added primary sealing component. The sealing component is either an unsupported, plastically flowing material or an elastic material at the liner edges. Both require added cost and may adversely affect reliability and safety.
None of the current or alternative approaches known to the inventors eliminates the problem of brittle liner edge sealing without risking liner damage (from excessive seal loads) or loss (with a plastic flowing material) of the seal. Even if in place and undamaged, the reliability of these lined joints appears to be limited.